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Comparison of in vitro-cultured and wild-type Perkinsus marinus. II. Dosing methods and host response
Marnita M Chintala1, David Bushek, Susan E Ford
1chintala.marty@epamail.epa.gov
Abstract:
Endoparasites must breach host barriers to establish infection and then must survive host internal defenses to cause disease. Such barriers may frustrate attempts to experimentally transmit parasites by 'natural' methods. In addition, the host's condition may affect a study's outcome. The experiments reported here examined the effect of dosing method and host metabolic condition on measures of virulence for the oyster parasite Perkinsus marinus. Oysters, Crassostrea virginica, were challenged with wild-type and cultured forms of P. marinus via feeding, shell-cavity injection, gut intubation and adductor-muscle injection. For both parasite types, adductor-muscle injections produced the heaviest infections followed by shell-cavity injection, gut intubation, and feeding. There was no difference in parasite burdens between oysters fed cultured cells by acute vs chronic dosing, and parasite loads stabilized over time, suggesting a dynamic equilibrium between invasion and elimination. P. marinus distribution among tissues of challenged oysters indicated that parasites invaded the mantle and gill, as well as the gut, which has been considered the primary portal of entry. Frequency distributions of P. marinus in oysters challenged with 3 different culture phases indicated an aggregated distribution among hosts and suggested that stationary-phase parasites were easiest for the oyster to control or eliminate and log-phase parasites were the most difficult. Host metabolic condition also affected experimental outcomes, as indicated by increased infection levels in oysters undergoing spawning and/or exposed to low oxygen stress.
Insights
Experimentally infecting oysters with Perkinsus marinus revealed that injection methods and host stress significantly impact parasite virulence. Adductor muscle injection led to the heaviest infections, while spawning oysters showed higher parasite loads.
Area of Science:
- Marine biology
- Parasitology
- Invertebrate pathology
Background:
- Endoparasites require breaching host barriers for infection and survival.
- Host condition can influence experimental outcomes in parasite studies.
- Perkinsus marinus is a significant oyster parasite impacting aquaculture.
Purpose of the Study:
- To investigate the impact of different dosing methods on Perkinsus marinus virulence.
- To assess the effect of host metabolic condition on P. marinus infection levels.
- To understand parasite distribution and host-parasite dynamics in Crassostrea virginica.
Main Methods:
- Oysters (Crassostrea virginica) were challenged with P. marinus (wild-type and cultured) using feeding, shell-cavity injection, gut intubation, and adductor-muscle injection.
- Parasite burdens and tissue distribution were quantified.
- Host metabolic condition was manipulated (spawning, low oxygen exposure).
- Different culture phases of P. marinus were used for challenge.
Main Results:
- Adductor-muscle injection resulted in the heaviest infections, followed by shell-cavity injection, gut intubation, and feeding.
- Parasite loads stabilized over time, suggesting a dynamic equilibrium.
- P. marinus invaded mantle and gill tissues, not just the gut.
- Stationary-phase parasites were easier for oysters to control than log-phase parasites.
- Oysters undergoing spawning or exposed to low oxygen showed increased infection levels.
Conclusions:
- Dosing method and host physiological state are critical factors influencing P. marinus experimental infections.
- Parasite distribution is broader than previously assumed, indicating systemic invasion.
- Understanding these factors is crucial for accurate virulence assessment and disease management in oysters.